traffic signals safety and efficiency project – stage two implementation

Traffic Signals

Safety and

Efficiency Project

– Stage Two

ImplementationNational AITPM Conference,

WA Presentations

20 August 2015

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The study looked at the Main Roads WA signal refinement processes by

examining two subject sites to identify:

• What signal treatments are currently utilised

• What signal improvements could be achieved

• Measures and methodology for signal timing refinement and

performance

• Main Roads WA signal refinement policy, management, and resources

Testing the use of an alternative method for optimising traffic signals to

squeeze more from existing infrastructure, this method being modelling with

integrated SCATS signal control.

Project Introduction

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Why do this study?

The dream:

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Why do this study?

The reality:

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What is SCATS?

Sydney Coordinated Adaptive Traffic System

• SCATS monitors traffic volumes in real-time and coordinates traffic signals.

• It adjusts the coordination and green time of signals depending on the

traffic volumes detected on each approach.

• Approximately 900 signalised SCATS intersections in WA

(VicRoads Traffic Management Centre. Photograph courtesy of VicRoads.)

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What is SCATS?

(Image courtesy of Google Street View.)

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Stage One:

• Information from the Main Roads WA workshops and other sources

• Review of the SCATS settings

• Micro-simulation models built with SCATS signal control

• Morning, Midday, Evening, and Off peak periods tested

Stage Two:

• On-site implementation of recommended SCATS settings

• Assessment and evaluation of AM and PM periods

Many subject sites were considered but two were selected for testing:

• Orrong Road Corridor

• Tonkin Highway/ Kelvin Road intersection

Project Methodology

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Tonkin Highway/ Kelvin Road Site Description

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Orrong Road Site Description

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Orrong Road Model

Orrong Road Model

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Option Testing Plan

Orrong Road Quantitative Analysis

Option Option Details

Option 1Determine the optimal cycle time and refine SCATS data which will include

operating incremental split selection

Option 2 Stagger the pedestrian crossing on Wright and Oat Streets

Option 3

On the south approach of Francisco Place implement a left turn only with a u-

turn bay on Orrong Road. At Archer Street and Wright Street implement a lag

right turn. SCATS data refined.

Option 4 Testing of Oats Street under a double diamond overlap operation

Option 5Ultimate test, as per Option 1 with further refinement to SCATS data and

coordination

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Percentage Change in Total Corridor Delay:


AM Midday PM Off-Peak Total

Option 1 -17.6% 25.8% 2.2% -7.0% -4.0%

Option 2 -2.4% 0.3% -7.8% 2.1% -3.7%

Option 3 -15.9% 2.4% 8.5% -7.8% -4.6%

Option 4 15.5% 8.0% 33.3% -2.5% 20.0%

Option 5 -16.8% 18.4% -13.2% -6.7% -10.0%

Equating this to annual delay cost to occupants, Option 5 would save

approximately $760,000 per year in lost time cost.

Carbon Emissions (grams):

AM Midday PM Off-Peak Total

Base 28,866 20,013 26,590 6,418 81,886

Option 1 26,786 20,953 27,641 6,038 81,419

Option 2 28,943 19,913 26,501 6,418 81,775

Option 3 27,273 19,776 28,161 6,044 81,255

Option 4 32,101 20,153 28,086 6,375 86,716

Option 5 27,546 20,484 26,614 6,092 80,736

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00:00

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02:00

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0 500 1000 1500 2000 2500 3000 3500

Trav

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Distance (m)

Westbound Journey Times - AM Peak

Base

Option 1

Option 2

Option 3

Option 4

Option 5

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01:00

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06:00

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0 500 1000 1500 2000 2500 3000 3500

Trav

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Distance (m)

Eastbound Journey Times - PM Peak

Base

Option 1

Option 2

Option 3

Option 4

Option 5

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Orrong Road Base Model at Francisco Street

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Orrong Road Option 5 Model at Francisco Street

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• Option 5, widespread incremental split selection and optimal cycle time

with refinement, has the largest improvement in terms of delay and

average speed

• Option 1, 2, and 3 are considered to have performed slightly better

than the base model overall

• While improvement can be found through changes to the SCATS signal

settings, the current phasing setup can not be further improved.

Orrong Road Options Results Summary

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• Pre-implementation assessment

• Recalibration and testing/ refinement of the option

• Trial Implementation

• On-site refinement

• Post-implementation assessment

• Evaluation Reporting

Stage Two: Orrong Road Implementation and

Evaluation

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Orrong Road Option 5 Implementation Process

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Orrong Road Option 5 Implementation Results

*Number of Queued Vehicles

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*Number of Queued Vehicles

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*Peak hour volumes

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*Peak hour volumes

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Stage Two Analysis Summary

• Vehicle throughput:

• up to 10% increase westbound, towards the Perth CBD, in the AM

period

• up to 3% increase eastbound, towards the Perth Hills, in the PM period

• Mixed travel time results:

• AM travel times remained relatively similar for both directions of travel

• PM period had a 20% decrease in travel times eastbound but a 16%

increase westbound.

• Overall mid-block and side roads queue lengths:

• 30% decrease in the AM period

• 34% decrease in the PM period

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Overall Study Summary

• The use of ISS can improve the performance of several Orrong Road

intersections (ISS allows for more dynamic behaviour of the SCATS signal

phase splits)

• The reduction in cycle lengths provide a more balanced outcome for delays

• The use of micro-simulation modelling allowed multiple options to be tested

with the best performing option selected to provide an improvement once

implemented on-site.

• Future studies regarding the performance of signalised intersections should

have clearer communication links and protocols in place regarding signal

changes

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Other Study Comments

• It is difficult to accurately allocate corridor benefits to individual SCATS settings.

• Higher cycle times allow increased periods of green time which can assist

slower vehicle types but these higher cycle times can lead to:

• Longer queue lengths, particularly on the side roads and in turn bays

• Increased delay for pedestrians.

• Increased driver inattention resulting in poor reaction times

• More red light running to avoid waiting for the next signal cycle

• SCATS setting changes should be assessed on a site by site basis depending

on the traffic patterns and the coordination with surrounding intersections.

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Modelling Comparison

• Shorter queue lengths observed for both the modelled and on-street scenarios.

• Some variation between the predicted model journey times and the on-street

journey times. Due to:

• The impact of the signal changes on pedestrian phase calls

• The impacts of minor private driveways

• On-street variability in the performance of heavy haul vehicles

• On-street traffic pattern variability

• Looking at the overall model predictions, the model predicted the improvement

in the corridor performance.

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SCATS Signals Optimisation

It is not just the signals fault!

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Driver Inattention

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The WA Space-Time Continuum

(Image Courtesy of Google Earth)

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Acknowledgements

RAC WA Policy and Research Team

- Anne Still, Senior Manager

- Una Mehta, Senior Traffic Engineer

- Sarah Macaulay, Transport Planning Manager

ATS – Bill Sissons

Main Roads WA TOC and Road Network Operations team

Aurecon – Steve Cotton, Peer Reviewer

Peter Kartsidimas - Initiation Team

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Thank You

(Image Courtesy of Wikipedia)

traffic signals safety and efficiency project – stage two implementation

Education